MUSTANG-1.5

MUSTANG-1.5 is a 64-feedhorn bolometer camera which will be commissioned
on the GBT in Winter 2014. Several features distinguish it from its
predecessor, MUSTANG:

A new, microstrip-coupled detector design will yield
higher sensitivity and less susceptibility to environmental
microphonics.

Detectors will be feedhorn coupled, with two linear polarizations
per feed (althought not designed specifically for polarimetry).

The instantaneous field of view will be 2.5 arcminutes (vs 40 arcseconds
for MUSTANG)

The receiver design incorporates a tilted refrigerator and receiver
rotator, resulting in much lower dependence of cooling performance on
telescope elevation.

The dewar, electronics, and receiver optics are straightforwardly
expandable to a much larger bolometer camera (MUSTANG-2), pending
funding.

The detector readout will be the first use of microwave resonators
to multiplex TES bolometers.

MUSTANG-1.5 is being built on a highly scalable platform to
facilitate construction of the final MUSTANG-2 camera: the
223-feedhorn, 4 arcminute diameter field of view camera ultimately
desired can straightforwardly use the existing optics, readout
electronics, and cryostat. MUSTANG-1.5 is being developed by a
collaboration including the University of Pennsylvania, NIST, NRAO,
the University of Michigan, and Cardiff University. It is being made
available on a shared-risk basis in current and upcoming proposal
calls; proposals require collaboration with the instrument team.

Some basic performance information is as follows:

The expected sensitivity of MUSTANG-1.5 on the GBT yields a 50
microJy RMS in one hour of integration time mapping a 4'x4'
region. The noise scales as the square root of the integration time up
to at least several hours; and the noise increases with the square
root of the area covered for larger areas. Mapping smaller areas is
not efficient in terms of noise performance. For photometry projects,
however, a center-weighted "daisy" scan pattern can be used which will
reduce the RMS noise by a factor of 1.9 on the central field of view
compared to what would be attained covering an equal area uniformly
for an equal total time. For significantly larger areas faster
scanning can be used which will reduce the noise by up to
35%. Proposals must explicitly state a target map RMS in order to
be evaluated for scheduling.

This sensitivity assumes an effective smoothing of 8" FWHM
provided (effectively) by the standard gridding kernel. If heavier
smoothing is acceptable the sensitivity is better by a factor of
(FWHM/8 arcsec).

Extended emission on scales of 30" to a few arcminutes can be
imaged with reasonable fidelity, but faint emission more extended than
this may be difficult to detect. Bright emission (20 mJy/beam or
more) can be reconstructed over scales of many arcminutes. The
angular resolution of MUSTANG on the GBT is tyipcally 9" (FWHM) and
the instantaneous field of view is 2'.5 x 2'.5.

Allowing for weather and calibration and observing overheads,
observers should conservatively allow an observing efficiency of 50%
(i.e., assume equal times integrating on source, and for calibrating
and general overheads - so 100% overheads relative to observing time).

Daytime observing at 90 GHz is currently not advised. The
changing solar illumination gives rise to thermal distortions in the
telescope structure which make calibrating 90 GHz data extremely
difficult. Useful 3mm observations are currently only possible
between 3h after sunset and sunrise.

We request that publications resulting from MUSTANG observations on
the GBT include the following acknowledgement: "The authors would
like to thank the MUSTANG instrument team from the University of
Pennsylvania, NRAO, Cardiff University, NASA-GSFC, and NIST for their
efforts on the instrument and software that have made this work
possible. ". Additionally, we request that you
cite Dicker
et al. (2008) in the paper text.
NRAO offers page charge support if you do a few simple things.

NEWS

MUSTANG-1.5 Arrives at the GBT (December 2, 2014)

MUSTANG-1.5 arrived in Green Bank and is preparing for first light on
the GBT later this month!

MUSTANG-2 is Under Construction!

MUSTANG-1.5 is currently being integrated and tested in the lab at
U.Penn., with first light on the GBT scheduled for winter 2014.

MUSTANG-2 Detectors delivered to U.Penn!

In June 2014 72 packaged detectors were delivered to U.Penn for testing and
characterization.

Left: Cutaway view of tapered feed design; Right: the final MUSTANG-2 feed horn array
as fabricated (223 feeds). The feed array weighs 8kg and has been successfully cooled
to 300 mK in the MUSTANG-2 cryostat.

Cutaway showing the design of the MUSTANG-1.5 receiver

Pictures of the receiver in the lab at U.Penn.

One ROACH board with its custom daughter cards for the microwave
resonator readout.

MUSTANG retired at the end of 2013

MUSTANG-- the original 90 GHz, 64 pixel GBT bolometer camera-- was
retired at the end of calendar year 2013 in anticipation of the
arrival of its successor, MUSTANG-1.5 MUSTANG proposals were accepted
from June 2009 through Feburary 2012.

New GBT Surface Improvements (Sept. 2009)

A concerted campaign of phase coherent holography measurements and
actuator repairs has resulted in further, remarkable improvements in
the GBT surface: the current Ruze-equivalent surface RMS is estimated
to be better than 275 microns rms! This means that MUSTANG should be
at least 50% more sensitive than it was for Spring 2009 observing. The
following image shows a sequence of surface maps made over the course
of the year.

(courtesy T.Hunter & F.Scwab, NRAO)

GBT Surface Improvements (July 2009)

The campaign of traditional, phase-coherent holography led by Todd Hunter & Fred Schwab is paying
off, having already yielded a factor of two improvement in the GBT 90 GHz aperture efficiency
with more improvements on the way. More information can be found in the February and May NRAO e-news.

Map of GBT surface irregularities before (left) and after (right) corrections
based on a series of holographic surface maps. The version numbers refer to
which set of surface corrections were in place at the time the map was made,
with higher numbers (e.g., v3.05) indicating more recent, better maps. (Image courtesy
of Todd Hunter & Fred Schwab, NRAO)

Scans across the moon at 46 GHz with the GBT with three different
sets of surface corrections in place on the telescope, showing the far
sidelobe response. The more recent telescope surfaces yield substantially
lower sidelobe levels, as expected. (Image courtesy of Todd Hunter & Fred Schwab, NRAO)

Scan through a calibrator source with MUSTANG showing the initial, 10%
efficient surface response (v1.3), and the improvement that results from
an early set of holographic surface corrections (v2.35). On this scale
the July 24 2009 map (v3.05) is expected to give a peak intensity of 2. (Analysis by Phil Korngut, U.Penn)

Real-time GBT Surface Updates

Using "out-of-focus" or phase-retrieval holography techniques, it is
possible to make real time measurements of the medium to large scale
aberrations in the GBT surface by analyzing in-focus and out-of-focus
beam maps of bright calibrator sources. Acquiring the data, analyzing
it, and applying the resulting corrections to the telescope surface
requires less than 15 minutes with MUSTANG, and the process is
essentially completely automated (requiring the user only to push a
button to accept & send the solution).

In focus (center) and two out of focus (left, right) maps of
a bright point source.

Left: GBT phase error map derived from the beam map data
above. Color scale is in radians; note that since MUSTANG only
illuminates the central r=45m, the phase at the outer edge of the dish
is unconstrained and not important observationally. Right: The beam
that results from applying the aperture phase corrections to the
telescope (on a slightly burned in scale, common to all four beam map
plots). Near-in sidelobe levels are lower and the peak foward gain is
typically increased by 20-30%.

Early Science Images

MUSTANG+GBT 90 GHz map of Orion on 3 color scales emphasizing the
dynamic range and sensitivity to extended structure that has been
achieved. These maps resulted from early science observations in
Spring 2008; the area covered is approximately 5'x10'.

MUSTANG+GBT map of Cas A collected during commissioning, January 2009.

MUSTANG+GBT large-area map of the W3 region (0.4 deg x 0.3 deg). This map required 45 minutes
to collect and was a test of MUSTANG's large-area mapping capability. Due to the high slew
speeds involve it is possible to suppress instrument and atmospheric "1/f" noise to a greater
extent than is possible when mapping smaller fields, resulting in a 25% improvement
in sensitivity.